This invention is directed to a biased seal bar for a form, fill and seal packaging machine. A biasing means is positioned between a seal bar and a support element whereby the seal bar can move against the bias of the biasing elements during a sealing operation to insure absolute parallel mating of the seal bar with a further seal bar.
A variety of products are packaged in film pouches which are formed, filled and sealed on appropriate packaging machines. These machines utilize continuous rolls of film. A pouch is formed from the film, filled with product and then sealed in a continuous operation.
To form pouches on a form, fill and seal pouch packaging machine, side seams are formed between front and back films via side seals. A cross seal is then utilized to form the bottom seam. This three sided pouch is then filled with product and the machine is indexed. A further cross seal is now utilized to form the top seam on this filled pouch and concurrently the bottom seam on the next partly formed but still empty pouch. The machine is indexed and the cycle continued.
Both the side seams and the cross seams (herein after also referred to as side seals and cross seals) are formed by opposing front and back seal bars which come together to pressurize and heat seal front and back rolls of film together. The heat and pressure forms a seal between the films to create the various pouch seams.
A typical pouch packaging machine is capable of concurrently forming a linear array of side by side pouches across the width of the machine. The number of side by side pouches which are concurrently formed can vary from a single pouch when large pouches are being formed to 16 to 20 pouches when narrower pouches are being formed, as for instance, condiment pouches. Thus, on a machine utilizing 24 inch film, concurrently 16 side by side one and a half inch condiment pouches can be formed.
The front and back cross seal bars on such machines come together across the width of the films which are being sealed together. This forms a seam. It is important that the sealing faces of these cross seal bars be very parallel to one another. With parallel cross seal bars, the seal formed between the films on one side, as for instance the left side, is formed under the same pressure as the seal formed on the other side, the right side of the film.
Since seams are formed in the film utilizing both heat and pressure it is necessary to heat the seal bars, both the side seal bars and the cross seal bars. Heating these bars inevitably leads to expansion. A typical film being sealed may be film that is from 1.0 to 1.5 mils in thickness. It is not uncommon for a cross seal bar to expand at least 1.0 mils when heated. While expansion across the width of the bar should be constant, there can be minor expansion differences between one side of a seal bar and its opposite side.
Presently used form, fill and seal packaging machines rely only on a threaded adjustment for positioning of the seal bars with respect to one another. To get front and back seal bars in perfect parallel alignment can require considerable trial and error adjustment. Even then an exact even pressure may not be applied across the total width of the seal bar. This arises because of minor differences which were not discernible to the operator when the seal bar were adjusted or because of uneven heat expansion of the seal bars during production runs.
An improperly formed seal in a pouch can lead to rupture of the pouch. This renders such a pouch useless. This, of course, detracts from the economics of operation of the form, fill and seal packaging machine. It is thus evident to maximize production of a form, seal and fill packaging machine it is important that perfect seals be formed- across the totality of the width of film during the production run of the machine.